Asbestos sheet material and method of manufacture



Patented Sept. 11, 1951 ASBESTOS SHEET MATERIAL'AN'D METHOD OF MANUFACTURE Harold W. Greider and Marion li. .fimith, ,=.Wy

mine, Dh a. assisnors to Th .Bh lip smite? Manufacturing Company, ,a corporation of Ohio N Drawing. ApplicatioxrDecember 29,1944,

SerialNo. 570,478

, This invention relatestoasbestosproduets and relates especially to products which compr s fibrous material containing asbestiformmineral fibers disposed in intimately contacting relation as by felting or other operationadapted to form a sheet or sheet-likebody.

The asbestos products which find mostextensive commercial use are asbestos, sheet materials that are usuallyiproducedby water laying and that, are generally referred to .as asbestos paper ,or asbestos mill board, which is referred to herein generally as fpaperf The bulk of the asbestiform mineral fiber that is used inasbestos paper usually runs fromabout 3%" t A" in length, although the fiber that is supp i d for paper making generallycontains a considerable quantity of shortenfibers of .Varying lengthsand may containa portionof lon er fibers. The most generally accepted system of classification of asbestos fibers ,is thatof the Quebec Asbestos roducersAssociation- Theasbestos fibe which are most commonly. used forthe manufactureof asbestos paperare those whichgran e from the Grou 5 or paper classification tothe Group 'Ior shorts classification of theQuebec AsbestosProducers Association, or mixturesthereof.

In the manufacture of asbestos paper from asbestos fibers of the character aforesaid, the fibers are water-laid in felted relation by a paper making operation, a multicylinder paper making machine generally being used for the purpose.

An asbestos paper of the character aforesaid has very little strength in the absence of a binder. Hydration by heating, as employed for the development of strength in cellulosic papers, is inelfective with the inorganic asbestos fiber and merely results in the shortening of the fiber with consequent actual loss ofrstrength of theresulting asbestos paper. The strength of the asbestos paper can be somewhat increased by the employment of asbestos fibers which are longer than the asbestos fibers usually used in the manufacture of asbestos paper. There are, however, objections to the use of long asbestos fibers in the manufacture of asbestospaper. In the first place, longa'sbestos fibers are of much higher cost and are usually reserved for spinning purposes. Asbestos fibers of intermediate length, namely, between the long spinning fibers andthe relatively short fibers used. for makingasbestos paper, are generally usedfor reinforcement purposes, e. g., as a reinforcement in the manufacture of heat insulation materials and the like which consist in major proportion of finely-diyided non-fibrous heat-resistant material that is Claims. (Cl.. 1,17- 12 6) reinforced Qby zthe asbestos fibers Another rea son .tvhythe=lonafibersare nQt:.-n e nthe manutacture of asbestos paper -is' th tact that l n fibers .are .idinicult toform int nn iorm-sheefes from the aqueous suspension in a aper-makin operati n, The lo g fibers tend to t rm :inte .clumpswhich;r sultein :theiorme inaper imelets of fiberwith thinor opensnacestdefieient f ber. therebetween. Moreover only a sli ht -increase in strength is afforded by the. emp oym nt of. loos asbestos fibers in the manufacture of bestos paper. This invention is v of: particular utility the manufacture of products item the more commonrand less exn nsivetflbersrof :the paper mak ng grades; mentionecl;above- .zlt. heretoforebeenstandard;nracticeinthe manufacture of as e tos reaper {to :usestamh as the binder materialior mpartin stren th tothe pending uponthe purpose for) which the-asbestos paperis intended.

,In addition to the starchrother organic binder materials have had limited use in connection with asbestos paper such as rubber latex and various synth tic rubber-lik mater v;-wh ich aregenerally referred to as elastomers. ,Qrdie nary organicub nders such, ascasein, soya, protein, glue, rosin and the like have, not been. found to be suitable for use in the manufacture of asbesto paper. ,Synthetie re inso varioustypes may be used as a binder for asbestosjfibers but their costvis extremely high and for this reason their use for most purposes is. not practical,

The use in stos paper or otherv asbestoscontaining products ,of an organic binder, material such as starch objectionable for several reasons. The most serious objectionis due to the fact-that an organic bindermaterial lacks the, hi h resistanc .tQheatthat is possessed by a'sbestiform mineral fibers andthat constitutes the .main r ason "for .use of such if bers instead of the muc le s .a e pen or ani fib rs. Asbestosffiber is capable ,of.withstandingsustained temperatures of about. 900? Fbto' 1000, F. without excessive d t r oration- Moreov asbestos .fi-' ber,.b ne. inor nic. is n n-combustible an can be xnosed d ct y toapflame withoutuburni s or smok n Qth r advantagesofjasbestos fiber wh ch make its ju desirable result from 1 the f ct that asbes os fiber .is na fected by water and is not; subject to rotting or other gradual deterioration due to moisture. Moreover, asbestos fiber is not subject to attack by organisms which result in mildew, mold, fungus growths or the like and is not attractive to, or destroyed by, vermin.

When an organic binder is used in conjunction with asbestos-fiber, its presence as a binder is disadvantageous since an organic binder lacks virtually all of the desirable properties of the asbestos fiber. An organicbinder, if present in an asbestos paper, will start to decompose gradually at temperatures as low as 250 F. during periods of prolonged exposure. Temperatures of 300 F. are actively destructive to organic binder materials contained in asbestos paper, while attemperatures of 350 F. an organic binder will char in a matter of a few hours time. At temperature of 400 F. and higher an organic binder will smoke and char immediately. When the organic binder in an asbestos paper or other productis disintegrated due to temperature conditions such as those above mentioned, it loses its effectiveness as a binder with the result that the asbestos product becomes lacking in strength to an excessive degree and goes to pieces. As a result of this fact, the use of asbestos paper containing starch or other organic binder material for heat insulation purposes has been limited to conditions such that only relatively mild temperatures are encountered, namely, temperatures under about 300 F. As far as the asbestos fiber itself is concerned, it could be used at considerably higher temperatures, namely, temperatures up to about 900 F; to 1000 F. and would have wide commercial utility for use at such temperatures, but no binder has heretofore been found which is suitable as a binder for asbestos paper and which will not disintegrate excessively at temperature above about 300 F.

The extent to which an organic binder is objectionable'because of its lack of resistance to heat depends in part upon the amount of binder that is used. If the amount of binder is relatively low, such as of the order of about 5% or less by weight of the asbestos paper, the binder will not burn so as to produce a flame but it will discolor and also will char and smoke in a manner that is objectionable. If additional organic binder is used, e. g. to by weight, the binder in the asbestos paper may actually burn with a free flame. Regardless of the amount of binder that is used, any organic binder, such as starch, rubber, glue, resin or the like, tends to give ofi suffocating fumes when heated, such fumes being a hazard to life and objected to by Underwriters Laboratories, Inc., and by the National Board of Fire Underwriters as dangerous to public safety. Moreover, some gases which are given off are combustible and may even be explosive and present a further hazard for this reason. The more gradual deterioration and disintegration of organic binder material, as a result of prolonged exposures to elevated temperatures will, of course, take place regardless of amount of binder that is employed.

Other objections to use of organic binders are lack of resistance to Water and moisture, rotting, molding, and unattractiveness to vermin.

Summarizing theforegoing, the use in paper or other products of asbestiform mineral fibers is highly advantageous due to the resistance of asbestiform mineral fibers to heat, to water, to rotting and other deteriorating influences. However, when organici binders are employed, the organic binders'are lacking in the characteristic .4 properties which make the use of asbestos fibers desirable and the uses to which the asbestos product can be put become limited due to the undesirable properties and limitations of the binder material used.

It is possible to use certain inorganic binders with asbestos fibers but the products which result from the use of inorganic binder materials have been limited to rigid and boardy products which are cementitious in character.

It has also been proposed to impregnate asbestos paper with soluble silicates, such as commercial sodium silicate solution, and then dry the resultant sheet, the silicate, upon drying, becoming of a hardened glass-like character so that the dried product is rigid, boardy and brittle, and cracks readily when flexed.

It is the principal purpose of this invention to bond together the fibers of an asbestos product without the use of an organic binder and without rendering the product stiff and boardy as is the case when substances such as Portland cement or soluble silicates are used as binder materials. It is a further purpose of this invention to afiord asbestos products such as asbestos paper, sheets or the like having high resistance to heat, moisture rot and other destructive influences. It is a further object of this invention to provide novel heat-insulation material, lumber-like products, and other products fabricated from sheets of felted asbestos fibers that have been interbonded according to this invention.

We have discovered that asbestiform mineral fibers which have been produced in the form of a felted sheet-like body can be bonded together by the interaction of the asbestiform mineral fiber with a solution of a water-soluble inorganic phosphate to form a coherent body that is flexible and porous but that has much more strength than an untreated sheet of felted asbestiform mineral fibers. The interaction that occurs between the solution of the Water-soluble inorganic phosphate and the asbestiform mineral fiber is not definitely understood, but appears to be specific between the substance of the asbestiform mineral fibers and water-soluble inorganic phosphate. Numerous other inorganic compounds do not have such effect and may even decrease rather than increase the strength of the felted sheet material. While there appears to be some action of the phosphate compound on the surface of the asbestiform mineral fiber which affords a bonding material that bonds the asbestiform mineral fibers together where they come into contact when the fibers are subsequently dried en masse, the asbestiform mineral fibers retain their characteristic fibrous character and the resulting felted sheet after treatment has the desired bibulous and flexible character of asbestos paper.

The manufacture of a strong and coherent asbestos paper without the employment of any organic binder according to this invention may be illustrated as follows. Asbestos fiber, which may be any of the usual paper grades of asbestos fiber heretofore used in the manufacture of asbestos paper products, is made up into an aqueous furnish according to conventional methods used in the manufacture of asbestos paper and the furnish is formed into sheet material on a papermaking machine in the usual way until an asbestos paper is produced having the ultimate thickness and weight desired. The paper thus produced is free of any binder and after it has been formed it is subjected to drying as by passing it over a plurality of drying rolls. According asap-35c to this invention, the asbestos paper, which has been formed and dried, has a solution of orthophosphoric acid, -H3PO4, for example, applied thereto by any suitable applicating means which may be in the form of a transfer roll contacting complete and is more uniform. After the acid has been applied, the paper is again dried as by passing it over the drying rolls which may be heated to conventional drying temperatures such as 200 to 300 F. although the degree of heating is in no way material and does not contribute to 'the successful manufacture of the new product. -If desired, the productmay be dried at ordinary atmospheric temperature. The dried paper may, for example, contain about 5% or less of retained moisture although the extent of drying is not critical- After the paper has been dried, it is ordinarily wound on a reel, trimmed to desired width, and made up into rolls as is conventional in paper-making operations.

The above-described process can advantageously be carried out in a single and continuous operation by applying the acid to the asbestos paper at an intermediate stage during the pas- "sage of the paper over the drying rolls of a conventional machine for the manufacture of asbestos paper products.

The concentration of the acid that is applied to the asbestos paper is not critical. Usually; the acid as applied is diluted with water so as to be of about'2% to about 30% concentration. The strength of the asbestos paper product is increased somewhat upon increasing the concentration of the acid that is'applied thereto up to a concentration of about 30%, but the amount of strength imparted in interbonding the asbestos weigh about ten pounds per 100 square feet, the resulting web or sheet when dried, and without having had any binder included in" the furnish has a tensile strength of only about two pounds per linear inch of width in the machine direction of the sheet and a tensile strength of only about one-half pound per linear inch across the sheet. Upon applying phosphoric acid of about concentration to the sheet material so that the sheet material will take up about seventy pounds of the diluted acid for each one hundred pounds of the asbestos sheet and then drying the .sheet. the resulting product has a tensile. strength in the machine direction of the sheet of about 14 pounds per linear inch of width and about 4 poundsper linear inch across the sheet. The tensile strengths that are given above and elsewhere herein are as determined by the method prescribed in A. S. T. M. standard D-202-41T using a Scott tensile testing machine, the test specimens of' paper having .been conditioned at 45% 6 relative humidityand 77 F; for four hours be fore testing.

A's'bestos-paperor other felted sheetdlke body wherein the-asbestiform mineral fibers have been bonded together by the interaction in situ between the asbestiform mineral fibers and the phosphoric acid, has the advantage of retaining its structural integrity and a substantial part of 'its dry strength when .contacted with water. A very severe accelerated test for determining the resistance of asbestos paper to water consists in immersing a small sample of the product (about -1-x 2 incheslin boiling water. Failure, if it occurs, is taken as the point at which the binder nolonger acts to hold the fibers together, the fibers becoming liberated to form a pulpy mass. "When subjected to the boiling water test, the paper, wherein the fibers had been bonded to.-

gether by the action of phosphoric acid, success;-

fully withstood the boiling water test for over minutes. The testwas discontinued at that time becausethe paper had not disintegrated and there was no indication that longer exposure to boiling water would result in disintegration. The high resistance to water that is afforded by the bonding together of the asbestiform mineral fiber by the action ofphosphoric acid thereon in situ is of great practical advantage in that asbestos paper having good wet strength can be readily produced. By comparison, ordinary asbestos paper which has been bonded-by means of starch has virtually no resistance to water and even when moistened with cold water immediately loses its strength and becomes reduced to a plastic pulp-like mass. While a water-insoluble binder such as rubber may be used in asbestos paper in order to afiord improved water-resistance, the higher cost of rubber is a practical disadvantage and, of course, rubber, being organic, tends to impair fire resistance and tends to give off malodorous smoke when heated.

In addition to phosphoric acid, other watersoluble inorganic phosphates are eifective in the practice of this invention to afford a bonded asbestos sheet or the like. Those water-soluble inorganic phosphates which, like phosphoric acid, provide a product having high resistance to water, and which are preferably employed in the practice of this invention are selected from the group consisting of phosphoric acid, sodium acid pyrophosphate, potassium acid pyrophosphate, sodium pyrophosphate, sodium phosphate (monobasic), sodium phosphate (tribasic), ammonium phosphate (monobasic), ammonium phosphate (dibasic), ammonium phosphate (tribasic),-potassium phosphate (monobasic), barium orthomonophosphate, magnesium hydrogen phosphate, chromium phosphate, aluminum acid phosphate, and magnesium biphosphate. Among these foregoing substances, the phosphates of ammonium and the pyrophosphate of sodium are especially effective. The magnesium hydrogen phosphate, above mentioned, constitutes an abbreviated designation for magnesium phosphate, which is normally insoluble, but which has been dissolved in the presence of about two molar equivalents of phosphoric acid. Other examples of water- 'soluble inorganic phosphates which provide a bonded sheet-like body comprising asbestiform mineral fibers according to this invention are aluminum acid phosphate, potassium pyrophosphate, potassium phosphate (dibasic), potassium phosphate (tribasic), sodium ammonium phosphate, sodium phosphate (dibasic), sodium metaphosphate, sodium hexametaphosphate, potassium 'metaphosphate, monofluorphosphoric acid, and difiuorphosphoric acid.

The foregoing substances are illustrative of those compounds which are referred to herein and in the claims as water soluble inorganic phosphates, namely, the hydrates of phosphorus pentoxid and the water-soluble inorganic salts of the hydrates of phosphorous pentoxide. The ,term hydrates of phosphorous pentoxide includes the several forms of phoshoric acid of which the most common are the ortho-, meta-v and pyrophosphoric acids and the term water soluble inorganic phosphates includes the water soluble inorganic salts of the above named acids. The term phosphoric acid as used herein and ,in the claims refers to any of the hydrates of phosphoric acid. The lower hydrates of phosphoric acid such as the metaand pyro-phosphates tend to hydrolyze when in water solution .to the ortho phosphate form. The substances monofluorphosphoric acid and difiuorphosphoric acid have been included in this category since these substances in water solution hydrolyze to form an equilibrium mixture containing phosphoric acid and hydrofluoric acid and, therefore, belong with the group of substances which is effective because of the special action of the hydrates of phosphorous peroxide.

The water-soluble inorganic phosphates listed above differ somewhat in effectiveness and for this reason the concentration of the solution that is appropriate for the different substances in the class varies but, generally speaking, is of the order that has been mentioned in connection with the employment of phosphoric acid.

After the treating step the residual dried binder material resulting from the treatment will desirably constituteless than 20% by weight of .the asbestiform mineral fiber. tion of flexible bibulous asbestos paper it is ordinarily desirable that the paper contain less than by weight of material other than the fiber and any finely-divided filler that may be contained therein.

According to this invention, asbestos paper can be readily manufactured which has ample .strength for the purposes to which asbestos papers are generally intended. Such paper can be readily handled and subjected to various treatments and will withstand deformation as in the manufacture of thermal insulation sheet materials comprising one or more layers of asbestos paper which has been corrugated or indented or has otherwise been deformed. When asbestos paper is prepared without any binder, its tensile strength in the machine direction is quite low, usually of the order of one to two pounds per linear inch .of width. An increase in strength which doubles the strength of the paper without any binder constitutes a considerable practical improvement although a tensile strength of at least five pounds per linear inch is ordinarily desirable. As pointed out above, considerably higher strengths can readily be attained according to this invention.

Asbestos sheet material can be made according to this invention which is notable not only ,for its strength but also for the fact that it re- ,mains flexible and bibulous. Thus, asbestos sheet material can be made according to this invention which takes up water or other liquid material as rapidly as asbestos paper which has been bonded with, for example, five to ten per cent of .starch. Typical embodiments of this invention will take up 30% or more of water and preferably For the preparaa 40% or more of water when immersed in water at 77 F. for five minutes. The flexibility of paper and other sheet materials made according to this invention is also important in enabling the paper to be fabricated into articles. In referring to sheet material as being flexible, it may be mentioned as typical that sheets having a thickness up to .050 inch or less may be bent around a mandrel of 1.5 inches diameter in two seconds at 77 F. without rupture or breaking at the surface and are thus of a suitable degree of flexibility for fabrication purposes.

Thin sheets are, of course, more flexible than thick ones and the flexibilily of the asbestos sheet material made according to this invention can, if desired, be further increased by calendering or other manipulative treatment of the sheet after it has been dried.

When the asbestos paper is treated with an acidic phosphate, such as phosphoric acid or an acid salt thereof, such treatment to which the asbestos paper is subjected according to this invention does not result in objectionable acidity of the product. Asbestos fibers are normally slightly alkaline and the alkalinity of the asbestos fibers eventually neutralizes any icidity which is imparted to the paper by the applied acid or acid salt so that the ultimate product is either neutral or of the slight alkalinity which is characteristic of any asbestos sheet consisting essentially of asbestos fibers.

It is apparent from the foregoing that a sheet, or other body of interbonded asbestos fibers, may be produced according to this invention which has substantial strength and which has the heat resistance and other properties of a product made essentially of asbestos. In other words, an asbestos product can be produced according to this invention which is essentially free of organic binder or other organic material and which is free from the objections that are incident to the presence of organic material in the product. The material may be subjected to sustained temperatures of 900 to 1000 F. without deterioration. Moreover, at such temperatures, or even higher temperatures such as flame temperatures, there is no charring, discoloration, or production of objectionable smoke or fumes. Moreover, the material is resistant to water and to moisture and is not subject to attack by organisms or vermin.

One of the uses to which the product of this invention is particularly adapted is use as or in heat insulation materials of various kinds. Thus the new asbestos paper by itself may be used as a protective covering for pipes, furnace walls and. the like and may be used even though temperatures as high as 900 to 1000 F. may be encountered. The new asbestos paper may also be used in the fabrication of composite insulation products. In such products, the new asbestos paper may, for example, be used as a surface layer. The new paper of this invention may also be utilized as the body portion of the heat-insulation .material.

In addition to the above, the new asbestos paper and sheet material of this invention may likewise be used in the manufacture of boardlike materials other than those especially designed for heat-insulation purposes.

It is also apparent that the new product of this invention, when made without employment of organic material contained therein, is superior to ordinary asbestos felt used in the manufacture of roofings such, for example, as build-up roofings which are commonly prepared using a plu-.-

' 1. product.

. .jected to very high temperature,.it.is.obvious that improved fireresistance canbeafforded by using as a base for roofing-the .new asbestos. sheet materialof thisinvention either-dry oryimpregnated -with a waterproofing material .such as a bituminous-material.

It :is not :necessary that .the .new -.product .of -this.invention be fabricated inthe manner above described,.namely, by the water-layingo'f a felted sheet -.of asbestos fiber-sand the application vof the treating compound .thereto. .Thus,1the asbestos .-.fibers :may be brought .into intimatelyassociated felted relationship ,in other ways :either wet or dry. In.this connection,.o.perations such as carding,.garnetting, and the like which accompl-ish adeposition .of fibers .toform a sheetlike body, are to be regarded as providing felted fibersas the term .felted.is.use'd herein and in the :claims. The momentof application of the .phosphate compound for reaction with the fibers is not .importantso long as the fibers as disposed inlfelted. relationare in .contact with -the treating substances. as contained in. an aqueous solution :and .thefelted fibers are permitted to dry eh I masse. so .that .the. bonding material occurringat the surfaces of the asbestiform min- :eral fiber will harden .and ,serve to .interbond" the asbestiform mineralfibers atthe points .of contact between the fibers. If desired, a plurality of .thin sheetsof asbestospaperorithe like to which lithe .treating compound has been applied and which isstill. inawetstate may. be. plied together so. as .toIform .a product consisting .of a plurality .ofplies, theplies being bonded together when ,..'dried-.by.thc. product of interaction between the :asbestiform mineral fibersandthe treatingcom- .pound.

.Intheordinary case, according to this inven- '.varieties of asbestosgnamely, anthophyllite, .ac-

tinolite, tremolite, crocidolite, amosite, various amphib'ole' fibers and .Canadian picrolite.

While it.isa. principal. advantageof this invention that an asbestos -productcan be produced .which..-is essentiallyfree .of organic material which .is. used eitheraas binder or as .part .of.the Jfibrous content of theproduct, the advantages .of

this invention maybe. availed of .even though some organic. material -may bepresent in the For example, an asbestos paper contain'ing'aminor amount of. organic fiber such as ordinarycellulosic. paper fiber may be subjected "toth'e phosphate-treating step'according to this invention and such-treatment will result in the,

"interbonding of the asbestos fibers in thesheet. I-Ioweverjformost purposesWhere high fire resistance is desired, a less than 5 by weight of the fibershOuld be-organicifiber. It-is possible toinclude in the asbestos-paper 'other mineral fibers Isuchvas rockfiwool; slag woolgi'glass. fibers and the 1 z-like'whichare'heat resistant, but such fibers have rthe ad'isadvantage of being more brittle and frangible than asbestos fibers. However,:in any event, ithes content of :iasbestos fiber should be sufilcient so that the asbestos fibers in the fibrous product come into intimate association, thereby permitting the asbestos fibers ,to become bonded together at a multiplicity of points of contact between the asbestos fibers for the creation of a bond between the asbestos fibers which imparts coherency and strength to the product as a whole. As apgeneral rule,the product produced according to this invention should consist in major proportion by weight .of asbestiform mineral fibers.

The new fibrous product of this invention as ordinarily made up for the market does not contain anyorganic binder. However, an organic binder may be applied depending upon themtended use of the product. Thus, while it is an advantage of this invention that the usual binder that is used in the manufacture of asbestos paper, namely, starch, may be omitted altogether, it is notwithout the scope of this invention to employ thespecial treating compounds in conjunction with starch. However, even in such case, it is normally desirable to take advantage of this invention by reducing the quantity of starch below that which is ordinarily used. Thus, for example, .the asbestospaper may contain 1% or less by weight of starch without detracting materially. from the heat resistance of the paperfor in such casethe paper, whenexposed to high temperature, may discolor to some extent but will not give 01f flame or an undue amount of smoke, and the paperwill retain its, bond notwithstanding the carbonization of the starch. These comments are equally applicable to other Or anic binders. .It is ordinarily desirable'that -the, as bestos paper .or the like be .made up employing less than 2% of organic binder. As mentioned above, an asbestospaper according to this invention may, for example, be impregnated with;a

bituminous saturant for various purposes. Other types of binder, which may or may notbe organic,.may be applied to the sheet material as in the manufacture. of gasket. material, brake linings and the.like. Moreovenuth'e product of this invention may. be impregnated with other types of bonding material such as soluble silicates which become hardened when dried andwhich may, if. desired, be insolubilized bysuch expedients as the use of. suitable insolubilizing agents or by heatcuring.

..In addition to the fiber and bonding components .of the products produced according to .thisinvention, the product may. include a minor .quantity .of .a finely-divided filler material. example, a small quantity, .e. g .,,of the order .of 5% to 10% ,.of the weight of the fiber, .of a material such as diatomaceous ,earth mna-ybeemployed. ..A filler such as diatomaceous earth ,.does,nothave .an adverse effect For on the porosity .and .absorptiveness of the paper and usually increases these properties. Another filler which .affords considerable porosity is finepumice. 'clay, talc, pigmentstoimpartv suitablecolor, etc. may 'beemployed. Whentheproduct of, this invention is designed to..be. resistant to. high tem- "peratures the filler material should beheat re- -sistant,- namely, should not decompose and char whenexposedtotemperatures .of the order of 1 900- F. Ordinarily, if .the.filler,.material, isheat resistant, an inorganic .filler ,is employed. Ordinarily, the major proportion by weightof the -fiber.plus .the. filler contained in the product should consistof .asbestiform mineral fibers and, forproyiding. resistanceto heat, the fiber plus anyfillerv should contain less than 10 of organic material or other non-heat resistant material.

Since the product of the invention can be made up so as to consist substantially of asbestos fiber, or asbestos fiber together with other heat resistant fiber or filler, the product can be exposed to temperatures such as 900 F. to 1000 F.

without injury. This is of considerable advantage in enabling asbestos paper products which have been impregnated with a soluble silicate to be heat cured at temperatures of the order mentioned to insolubilize the silicate. If ordinary asbestos paper containing an organic binder were to be subjected to such heat curing temperatures, the paper would become discolored, charred and weakened and an unsatisfactory product would result.

For most purposes where resistance to exposure to high temperatures is desired, it is desirable to produce the product of this invention so as to be substantially free of any organic material. This is also desirable in order to afford high resistance to rotting, mildew, etc. However, about 6% by weight oforganic material can be tolerated in the product while still affording these attributes in an unusually high degree.

While this invention has been described in connection with certain typical examples of the practice thereof, it is to be understood that this has been done merely for purposes of illustration and that the scope of this invention is to be defined bythe language of the following claims.

We claim: 1. As an article of manufacture a flexible coherent bibulous felted-fiber sheet-like body, said fibers comprising asbestos fibers which are interbonded in situ by the interaction of said asbestos fibers in situ as disposed in felted relation in said sheet-like body with a water-soluble inorganic phosphate.

2. As an article of manufacture a flexible coherent bibulous felted-fiber sheet-like body according to claim 1 wherein said sheet-like body contains less than 2% by weight of organic binder.

3. As an article of manufacture a flexible coherent bibulous felted-fiber sheet-like body according to claim 1 wherein the water-soluble inorganic phosphate is selected from the group consisting of phosphoric acid, sodium acid pyrophosphate, potassium acid pyrophosphate, sodium pyrophosphate, sodium phosphate (monobasic), sodium phosphate (tribasic), ammonium phosphate (monobasic), ammonium phosphate (dibasic), ammonium phosphate (tribasic), potassium phosphate (monobasic), barium orthomonophosphate, magnesium hydrogen phosphate, chromium phosphate, aluminum acid phosphate, and magnesium biphosphate.

4. A flexible coherent bibulous felted-fiber sheet-like body which consists in major proportion by weight of asbestos fibers and which contains less than about 6% by weight of organic material, said asbestos fibers being interbonded in situ by the interaction of said asbestos mineral fibers in situ as disposed in felted relation in said sheet-like body with a water-soluble inorganic phosphate, and said sheet-like body containing less than by weight of material other than fiber plus any finely-divided filler container therein;

5. A flexible coherent bibulous felted-fiber sheet-like body according to claim 4 wherein the water-soluble inorganic phosphate is selected from the group consisting of phosphoric acid,

sodium acid pyrophosphate, potassium acid pyrophosphate, sodium pyrophosphate, sodium phosphate (monobasic), sodium phosphate (tribasic), ammonium phosphate (monobasic), ammonium phosphate (dibasic), ammonium phosphate (tribasic), potassium phosphate (monobasic), barium orthomonophosphate, magnesium hydrogen phosphate, chromium phosphate, aluminum acid phosphate, and magnesium biphosphate.

6. As an article of manufacture a flexible bibulous felted-fiber asbestos paper wherein asbestos fibers constitute the major proportion by weight of the fiber plus any filler contained in said paper, said asbestos fibers being interbonded in situ by the interaction of said asbestos fibers in situ as disposed in felted relation in said feltedfiber asbestos paper with a water-soluble inorganic phosphate to provide a tensile strength of at least about 5 pounds per linear inch for the said flexible and bibulous asbestos paper which for sheet thicknesses up to 0.05 inch is bendable around a 1.5 inch diameter mandrel in 2 seconds at 77 F. without rupture or breaking at the surface.

'7 As an article of manufacture a flexible bibulous asbestos paper according to claim 6 wherein any organic fiber plus any organic binder constitutes less than 10% by weight of the fibers plus any finely divided filler contained in said paper and which contains less than 15% by weight of material other than fiber plus any finely-divided filler contained in said paper.

8. As an article of manufacture a flexible bibulous asbestos paper according to claim 6 which contains less than 6% byweight of organic material.

9. As an article of manufacture a flexible bibulous asbestos paper according to claim 6 which is substantially free of organic material.

10. As an article of manufacture a flexible bibulous felted-fiber asbestos paper wherein asbestos fibers constitute the major proportion by weight of the fiber plus any filler contained in said paper, said asbestos fibers being interbonded in situ by the interaction of said asbestos fibers in situ as disposed in felted relation in said felted-fiber asbestos paper with a water-soluble inorganic phosphate selected from the group consisting of phosphoric acid, sodium acid pyrophosphate, potassium acid pyrophosphate, sodium pyrophosphate, sodium phosphate (monobasic), sodium phosphate (tribasic), ammonium phosphate (monobasic), ammonium phosphate (dibasic), ammonium phosphate (tribasic), potassium phosphate (monobasic), barium orthomonophosphate, magnesium hydrogen phosphate, chromium phosphate, aluminum acid phosphate, and magnesium biphosphate to provide a tensile strength of at least about 5 pounds per linear inch of width for said flexible and bibulous asbestos paper which for sheet thicknesses up to 0.05 inch is bendable 180 around a 1.5 inch diameter mandrel in 2 seconds at 77 F. without rupture or breaking at the surface.

11. As an article of manufacture a flexible bibulous asbestos paper according to claim 10 wherein any organic fiber plus any organic filler constitutes less than 10% by weight of the fibers plus any filler contained in said paper.

12. As an article of manufacture a flexible bibulous asbestos paper according to claim 10 which contains less than 6% by weight or oganic material.

13. As an article of manufacture a flexible bib- 13 ulous asbestos paper according to claim which is substantially free of organic material.

14. A product comprising felted fibers disposed in a sheet-like body, a major proportion by weight of the fiber plus any filler contained in said sheetlike body consisting of asbestos fibers, said ashestos fibers being interbonded in situ by the interaction of said asbestos fibers in situ as disposed in felted relation in said sheet-like body with a water-soluble inorganic phosphate, said sheetlike body being impregnated with a bituminous waterproofing material.

15. A product according to claim 14 wherein any organic material other than said bituminous waterproofing material constitutes less than 10% by weight of the fiber plus any filler contained in said sheet-like body.

16. A flexible, bibulous felted-fiber asbestos paper consisting in major proportion by weight of asbestos fibers interbonded in situ by the interaction of said asbestos fibers in situ as disposed in felted relation in said felted-fiber asbestos paper with a solution of phosphoric acid, any organic material contained in said asbestos paper constituting less than 10% by weight of the fiber plus any filler contained in the asbestos paper.

1'7. A flexible, bibulous felted-fiber asbestos paper consisting in major proportion by weight of asbestos fibers interbonded in situ by the interaction of said asbestos fibers in situ as disposed in felted relation in said felted-fiber asbestos paper with a solution of a phosphate of ammonium, any organic material contained in said asbestos paper constituting less than 10% by weight of the fiber plus any filler contained in the asbestos paper.

18. A flexible bibulous felted-fiber asbestos paper consisting in major proportion by weight of asbestos fibers interbonded in situ by the interaction of said asbestos fibers in situ as disposed in felted relation in said felted-fiber asbestos paper with a solution of a pyrophosphate of sodium, any organic material contained in said asbestos paper constituting less than 10 by weight of the fiber plus any filler contained in the asbestos paper.

19. In the manufacture of a flexible, bibulous coherent sheet-like body of felted fibers consisting in major proportionby weight of asbestos fibers, the steps comprising contacting the asbes- 5 tos fibers while disposed in said sheet-like body of felted fibers with an aqueous solution of a water-soluble inorganic phosphate, said asbestos fibers being initially contacted with said aqueous solution of a water-soluble inorganic phosphate after the fibers in said felted-fiber sheet-like body have been disposed in felted relation in said sheet-like body, and thereafter drying the sheetlike body of felted fibers, thereby bonding together the contacting asbestos fibers in said sheet-like body by interaction in situ between said asbestos fibers as disposed in felted relation in said sheet-like body and said water-soluble inorganic phosphate, said solution of said watersoluble inorganic phosphate being applied at such concentration that said sheet-like body after drying is flexible and bibulous.

20. In the manufacture of a flexible, bibulous coherent sheet-like body of felted fibers consisting in major proportion by weight of asbestos fibers, the steps according to claim 19 wherein said Water-soluble inorganic phosphate is selected from the group consisting of phosphoric acid, sodium acid pyrophosphate, potassium acid pyrophosphate, sodium pyrophosphate, sodium phosphate (monobasic), sodium phosphate (tribasic) ammonium phosphate (monobasic), ammonium phosphate (dibasic), ammonium phosphate (tribasic), potassium phosphate (monobasic), barium orthomonophosphate, magnesium hydrogen phosphate, chromium phosphate, aluminum acid phosphate, and magnesium biphosphate.

HAROLD W. GREIDER. MARION F. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,690,079 Seigle Oct. 30, 1928 1,820,538 Kennedy Aug. 25, 1931 1,962,577 Wolochow June 12, 1934 2,034,522 Loetscher Mar. 17, 1936 2,128,097 Mains Aug. 23, 1938 2,237,745 Musgrave Apr. 8, 1941 2,348,829 MacArthur et a1. May 16, 1944 FOREIGN PATENTS Number Country Date 440,409 Great Britain Dec. 30, 1935 

19. IN THE MANUFACTURE OF A FLEXIBLE, BIBULOUS COHERENT SHEET-LIKE BODY OF FELTED FIBERS CONSISTING IN MAJOR PROPORTION BY WEIGTH OF ASBESTOS FIBERS, THE STEPS COMPRISING CONTACTING THE ASBESTOS FIBERS WHILE DISPOSED IN SAID SHEET-LIKE BODY OF FELTED FIBERS WITH AN AQUEOUS SOLUTION OF A WATER-SOLUBLE INORGANIC PHOSPHATE, SAID ASBESTOS FIBERS BEING INTIALLY CONTACTED WITH SAID AQUEOUS SOLUTION OF A WATER-SOLUBLE INORGANIC PHOSPHATE AFTER THE FIBERS IN SAID FELTED-FIBER SHEET-LIKE BODY HAVE BEEN DISPOSED IN FELTED RELATION IN SAID SHEET-LIKE BODY, AND THEREAFTER DRYING THE SHEETLIKE BODY OF FELTED FIBERS, THEREBY BONDING TOGETHER THE CONTACTING ASBESTOS FIBERS IN SAID SHEET-LIKE BODY BY INTERACTION IN SITU BETWEEN SAID ASBESTOS FIBERS AS DISPOSED IN FLETED RELATIONN IN SAID SHEET-LIKE BODY AND SAID WATER-SOLUBLE INORGANIC PHOSPHATE, SAID SOLUTION OF SAID WATERSOLUBLE INORGANIC PHOSPHATE BEING APPLIED AT SUCH CONCENTRATION THAT SAID SHEET-LIKE BODY AFTER DRYING IS FLEXIBLE AND BIBULOUS. 